1. Field of the Invention
The present invention relates to liquid fuel reformation and more particularly to systems and methods for reforming liquid fuels for use in fuel cell systems.
2. Description of the Related Art
As a society, we often take for granted the mobility (power and range) afforded by the energy storage density of common transportation fuels such as gasoline, aviation kerosene, and diesel fuel. The legacy investment in the refueling infrastructure alone makes it apparent that fuel cell technology capable of utilizing these existing fuels may have a distinct advantage over those restricted to high purity hydrogen or other less widely available fuels. The ability to utilize reformate produced from these existing transportation fuels, as well as from emerging non-petroleum based fuels such as bio-diesel, and synthetic (Fischer-Tropsch) liquids, without the need for extensive cleanup is one of the greatest advantages of solid oxide fuel cells (SOFCs).
The higher efficiency of fuel cells compared to conventional engines is one of the main characteristics motivating the development and eventual commercialization of fuel cells. In stationary applications, utilizing natural gas fuel, this efficiency advantage is well established. However, where liquid fuels are used, a fuel processor used to reform liquid fuel exacts a heavy efficiency penalty on a fuel cell system. Historically, the sulfur and aromatic content of transportation fuels has made them impossible to reform using the catalytic steam reforming process used with natural gas systems, due to problems with “poisoning” the catalyst and carbon buildup. Instead, partial oxidation processes (e.g., POX, CPOX, ATR, etc.) have been employed, with varying degrees of practicality.
Although reformate produced by partial oxidation typically represents about 80% of the energy content of the fuel as measured by heating value, the use of any partial oxidation process coupled to any type of fuel cell results in a loss in the range of 30 to 40% of the electric power generation potential of the fuel. This is primarily due to the fact that a fuel cell is not a heat engine. Rather, a fuel cell may be considered a Faradaic engine, and the Faradaic (current producing) potential of any fuel cell is reduced by 4 Coulombs for each mole of O2 introduced in the partial oxidation process. Although steam reforming does not suffer from such an effect, no suitable catalysts are known for high-sulfur, hydrogen-lean transportation fuels.
In view of the foregoing, what is needed is an improved system and method for generating reformate from various fuels that improves the Faradaic efficiency of fuel cells, such as solid oxide fuel cells (SOFCs), molten-carbonate fuel cells (MCFCs), or phosphoric acid fuel cells (PAFCs). Ideally, such a system and method would be capable of reforming fuels with high sulfur content (e.g., 10,000 ppm) without requiring sulfur pre-removal, while avoiding problems such as “poisoning” the catalyst or carbon buildup. Further needed is system and method for utilizing the heat generated by fuel cells such as SOFCs and MCFCs to improve the overall efficiency of fuel reformation and electricity production.